Conferencia; 29th ICPS - International Conference on the Physics of Semiconductors; 2008

Resumen:

A recent example of the successful combination of hyperfine techniques and ab initio calculations to unravel structural characterizations in the atomic scale of impurities in solids has been the study of SnO:Cd [1], where ab initio calculations questioned previous PAC assignments [2] of the electric-field gradient (EFG) at 111Cd-implanted in Sn-O thin films. As these samples were initially amorphous, they did not allow a reliable characterization of the impurity at defect-free cation sites of the SnO crystal structure, which is essential in order to extract valuable physical information of the doped-semiconductor from the ab initio calculations such as the impurity charge state, structural atomic relaxations, impurity energy levels, etc.
In this work, we present a series of gamma-gammaPerturbed-Angular Correlation (PAC) experiments with 111In-difused in polycrystalline SnO in order to measure the EFG at [111In (EC)à] 111Cd impurities at the defect-free cation site of the SnO crystal structure. The PAC measurements were performed in the temperature range 10-1000K in Ar (10-3 Torr) after a diffusion process of the probes, also monitored by PAC. Two hyperfine interactions were observed at high measuring temperatures (higher than 700 K), both with low distributions, low asymmetry parameters (as predicted by the crystal symmetry) and similar quadrupole frequencies (i.e., EFG´s). A strong damping of the perturbation functions was observed in the temperature range from 400 K to 600 K, assigned to the presence of dynamic hyperfine interactions. These experimental results are compared with those coming from a deep theoretical study (structural relaxations, impurity charge state, impurity levels introduced in the band gap of the semiconductor, etc.) performed with both the Full-Potential Linearized Augmented Plane Wave (FP-LAPW) and the Projector Augmented Wave (PAW) methods, in the framework of the Density Functional Theory, using larger supercells than that used in Ref. [1] in what respect to the first method. The excellent agreement between the experimental EFGs and the calculated ones let us to infer that different electronic surroundings around Cd impurities located at cation sites can coexist in the SnO sample and to correlate the presence of the dynamic interactions with the EFG dependence on the charge state of the impurity. [1] L.A. Errico, M. Rentería, and H.M. Petrilli, Phys.Rev. B 75, 155209 (2007).
[2] M. Rentería, A.G. Bibiloni, M.S. Moreno, J. Desimoni, R.C. Mercader, A. Bartos, M. Uhrmacher and K.P. Lieb,J. Phys. - Condens. Matter 3, 3625 (1991).